Darmstadt 2008 – wissenschaftliches Programm
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HK: Fachverband Physik der Hadronen und Kerne
HK 33: Hauptvorträge
HK 33.2: Hauptvortrag
Donnerstag, 13. März 2008, 11:30–12:00, 1A
e+e- pairs: a clock and a thermometer of heavy ion collisions at RHIC — •Alberica Toia — Stony Brook University, Stony Brook, NY, USA
Electromagnetic probes are ideally suited to investigate the hot and dense matter produced in high energy nucleus-nucleus collisions. Since they do not undergo strong interaction in the final state, they probe the whole time evolution and dynamics of the collision. Low-mass dileptons are expected to provide information on the early stage of the relativistic heavy-ion collisions which may experience an onset of deconfinement or chiral symmetry restoration.
The PHENIX experiment at RHIC has measured the dielectron continuum in p+p, Cu+Cu, and Au+Au reactions at √sNN = 200 GeV. While p+p and heavy ion collisions with a small number of participating nucleons (Npart) agree well with the known hadronic sources, central Au+Au collisions with Npart > 150 show an enhanced yield in the low mass region. The enhancement increases faster with the centrality of the collisions than Npart, suggesting emission from scattering processes in the medium.
While the mass dependence is important for an understanding of in-medium changes of light vector mesons and is insensitive to collective expansion, the pT dependence arises from an interplay between emission temperature and collective transverse flow and provides information on the temperature of the system and the duration of the different phases of the collision effectively resulting in a kinematical constraint of the phase diagram.